Method for making building panels



Jan. 22, 1963 G. L. WOLFE 3,074,157 METHOD FOR MAKING BUILDING PANELS Filed March 4, 1959 /NVENTOf? GILBERT L WOLFE Br 4 6. W

H/s ATTOHNE Y United States Patent 3,074,157 METHOD FOR MAKING BUILDENG PANELS Gilbert L. Wolfe, 9 40 Balltown Road, Schenectady, FLY. Filed Mar. 4, 1959, Ser. No. 797,141 2 Claims. (Cl. 29-469) This invention relates to an improved monocoque panel for a prefabricated building structure, and more particularly it relates to a manufacturing process for economically producing a stressed skin work-hardened self-sustaining panel which effectively combines load-bearing and sheltering functions in a single member using a minimum of material.

The load-bearing properties of a complex curved surface such as that found in an eggshell have long been recognized. It is also recognized that the yield strength of a metal may be appreciably increased by *cold working the metal in the plastic region beyond its elastic limit. Uses have been made in the past of the superior load-bearing characteristics of complex or multidirectional curved surfaces in building structures. These have generally been produced in their already complex shape, however, such as by casting or pouring a hardenable liquid into a mold as in the case of concrete, or by simply building the complex structure up from a number of individually shaped members having good structural characteristics.

The desire to achieve such a complex surface economically with sheet metal, because of its desirability as a building material, has led to many suggestions, such as corrugating the metal in a plane transverse to the plane of bending so as to give the overall effect of bending in two directions at one time. Although this has been partially successful, it will be appreciated that this is only an approximation of a true compound-curved smooth surface, and the presence of the corrugations makes the structure inherently non-rigid in at least one plane. Moreover, the

ethod of corrugating the metal sheets is wasteful of material and involves intricate bending or roll-forming apparatus which may not bring about the full benefits of work hardening in the final structure.

The obvious desirability of a monocoque or single skin panel which would be self-supporting and which could be manufactured out of a relatively light gage piece of sheet metal, led to the conception of a method for producing such a monocoque panel in a shape which makes use of the superior load-bearing characteristics of a complex surface and which at the same time effectively utilizes cold working and intentionally induced cold set internal forces to provide a structure of unusual strength.

Accordingly, an object of the present invention is to provide an improved monocoque self-sustaining panel which can be used in connection with similar panels to form a light-weight prefabricated building structure.

Another object of the invention is to disclose a process for forming the monocoque panel in a novel configuration which combines the utilization of cold set internal forces with the utilization of a complex surface to greatly increase the strength of the panel.

A still further object is to provide a prefabricated building structure which is simple to erect, economical to produce and transport, which has a high strength-weight ratio, which needs no beams or internal supporting members, and which has relatively few parts to assemble.

Generally stated, the invention is practiced by utilizing the process of stretch-forming to form a sheet of fairly ductile metal, such as aluminum, into a shape of complex curvature so as to cold work the metal to increase the tensile strength and to produce locked-in tensile forces in grain structure of the metal sheet. The configuration of the resulting panel is such that it is adapted 3,374,157 Patented Jan. 22, 1963 to resist bending in directions opposite to its compound curvature and such that it is ideally suited for securing to adjacent panels formed in the same manner to give an extremely rigid and efiicient building structure.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. My invention, however, both as to organization and method of opera tion, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is a horizontal elevation drawing showing the preferred methd of fabrication on a stretch-forming machine and showing an edge view of the panel as it is formed over the complex die;

FIG. 2 is a cross-section view taken along line 2-2 of P16. 1;

FIG. 3 is perspective view of an assembled building structure using a number of my improved monocoque building panels;

PEG. 4 is a detailed view of the joint between panels in FIG. 3, showing one method of securing adjacent panels; and

FIG. 5 is a detailed view of a modified panel joint.

Referring now to PEG. 1 of the drawing, a stretchformer 1 is shown in the process of stretch-forming a metal sheet 2 over a die 3. Stretch-forming has found some popularity in the aluminum industries due to the relative ductility of the metal. One of the principal advantages in using stretch-forming is that the troublesome problem of spring-back is practically eliminated, since all areas of the metal are stressed in tension beyond the elastic range.

The stretch-former 1, by which this process is accomplished, is shown in simple diagrammatic form in FIG. 1 as comprising a vertically movable die table 4 which is caused to be raised by hydraulic cylinders 5 disposed beneath the die table. A pair of jaws 6, '7, which are adapted to tightly grip the metal sheet 2 by means of hydraulically operated clamps 6a, 7a, are supported by head assemblies 8, 9 respectively. laws 6, 7 are individually movable in the head assemblies 8, h by virtue of being mounted on the ends of hydraulic pistons 11.1, 12 respectively. The head assemblies 8, 9 are supported by horizontally movable slides 13, M, and are arranged so that they can pivot in a vertical plane about the pinned connections 15, 16 when actuated by gears 17, 18 in a manner which will be obvious from the drawing.

It will be appreciated that the stretc -former 1 may be adjusted to the position as shown in FIG. 1 so that the die table 4 will exert an upward force on die 3 against the surface of the metal sheet 2, while at the same time, the jaws 6, 7 acting at the proper angle as shown, will grip the opposite ends of the sheet 2 to provide a reaction force resisting the upward movement. The stretch-former l is constructed to exert a powerful force on the work piece which may be in the nature of 60 tons to 300 tons or more and which causes the metal to be stressed in tension beyond the elastic range. It is understood, of course, that this forming operation takes place at normal temperatures rather than elevated temperatures. Upon exceeding the elastic range the sheet will undergo plastic deformation to stretch or elongate in the longitudinal direction. The metal will slide over the smooth working surface of the die 3 and attempt to attain the configuration of the die surface.

FIG. 2 shows a transverse section through the metal sheet 2 and a portion of the die 3 which will illustrate the novel manner in which the stretch-forming process is utilized to provide locked-in tensile forces in the monocoque'panel, the purpose of'which will 'be later described. There it will be seen that, in addition to the primary arch defined by the die and extending from jaw 6 to jaw 7 in FIG. 1, the die is transversely arched to form a generous curvature or secondary arch in the transverse direction which spans the distance between the sidewalls 3a of the die. As the sheet 2 is stretched in the longitudinal direction to form the primary arch illustrated in FIG. 1, the tendency of the metal to contract transversely as it elongates, coupled with the inwardly directed component of the stretching force and the outward pressure in the middle of the sheet, causes the outer edge portions 211 of the sheet to curl inwardly toward the radial portions 3a of the die. This causes the secondary arch to be formed in a plane transverse to the curvature of the primary arch. The resulting panel exhibits great strength and rigidity in resistance to bending from all outward directions.

As mentioned previously, the use of stretch-forming stresses all areas of the metal in tension beyond its elastic limit, while at the same time it produces the bidirectional arches. The cold working, or stretching, of the metal into this shape produces a piece which has been work hardened to increase the tensile strength, i.e. the shaping and cold Working occur simultaneously. Such a shape, if it could be produced by roll-forming or bending techniques, where the metal is not formed while held in tension but is merely bent 'angularly, would require very costly tooling in a complicated series of operations; and furthermore, in such a series of operations the metal cannot be uniformly shaped and simultaneously stressed or work hardened to produce the relatively high tensile strengths desired in the finished configuration.

Thus, the shape I have achieved is one which, in itself, on account of its bi-directional curvature, has great resistance to inward pressure from all directions. In addition to achieving this desirable shape, moreover, coldworking the entire area of the original sheet in the varying directions desired produces a tensile strength which would be difficult to achieve by other methods. For example, while metal stamping in a conventional press could also produce a high tensile strength, the punch could not easily be withdrawn from a continuously arched single panel such as illustrated in the preferred shape of FIG. 1, due to the fact that the primary arch extends more than 180 in order to increase the useful space inside the structure and in order to reduce side thrust on the foundation Walls.

As mentioned previously, the use of stretch-forming stresses all areas of the metal in tension. In addition to the cold working effect, it is felt that the strength of the panel may be increased still further by the following phenomenon. ere the stretching is elfected in the curved plane of the primary arch, the outer fibers on the convex surface 2b will be elongated more than the outermost fibers on the concave surface 2c since the total distance is greater due to the thickness of the metal. By use of a die which has a generous curvature in the transverse dircction as well as in the primary longitudinal direction, the outer edges 2a, as they curl in around the die under the action of the stretching force, will also stress the outermost fibers in the transverse direction.

Thus it can be seen that the convex surface 2b of the sheet will be subjected to increased elongation over that of concave surface 20, and that this increased elongation will exist both in the longitudinal direction along the primary arch and in the transverse direction along the secondary arch. Upon relaxing the force on sheet 2 and disengaging jaws 6, 7, this bi-directional curvature will manifest itself by constituting convex surface 2b much as a stretched membrane whereby locked-in tensile forces will exist in the convex surface 2b of the sheet. The bi-directional curvature of the sheet will prevent the sheet from flexing in order to relieve itself of these internal forces. When the panel is loaded, any forces which would ordinarily place the'fibers in the convex surface in compression, act first to relieve the internal tensile stress thus reducing the wrinkling tendency of a thin walled member under compressive stresses.

A preferred use of my improved novel monocoque building panel may be illustrated by reference to FIG. 3 of the drawing. There may be seen a partially assembled structure comprising adjacent panels 2, 2'', etc, which have been manufactured to the desired dimensions by the process illustrated in FIGS. 1 and 2. The assembled panels may be used to form a simple roof structure by securing them to the tops of opposite walls by some suitable means. a complete wall-and-roof structure, in order to achieve the most economical enclosure possible. it may be noted from the drawings in FIGS. 1 and 3 that the feet of the primary arch are closer together than the sides of the arch at its widest point. The purpose of this is twofold. First, the configuration results in a better utilization of space, since the headroom is not diminished, as it would be if the arch curved inward immediately. Of perhaps greater importance is the fact that the outward thrust on the foundation walls due to deformation of the panel under a load is counteracted by the inwardly directed components produced by the converging of the panel feet, which will reduce, it not entirely eliminate the net outward thrust on the foundation walls. The bottom edges 29 of the panels are secured to a ground-level support such as a concrete footing 2.1 by a suitable means, for example, anchor bolts and angle brackets properly shaped and drilled for this purpose (not shown).

Reference to FIG. 4 will disclose a suitable method of connecting adjacent panels. The extending flange portions, 2a, 2a" of adjoining panels 2, 2" perform a dual function in keeping with the simplicity of the novel structure illustrated. In addition to providing an extending flange surface in the radial direction which acts as a strengthening girder to improve the resistance to bending, these flange portions also provide convenient relatively flat abutting surfaces for fastening the panels together. This is illustrated by the use of expandable pin fasteners of a suitable material such as nylon, one of which is shown at 22. These are spaced at intervals around the primary arch and serve to hold the structure rigidly together. It will be appreciated that the expandable fastener 22 is shown for purposes of illustration only, and that many other methods of fastening, such as welding, bolting or riveting, could be used to hold the panels firmly together.

In order to deaden the sound transmission between panels, and to provide a seal, a flexible gasket 23 of some compressible material such as neoprene sponge rubber may be employed, although the use of a gasket is by no means mandatory. A putty or mastic 24 in the joint between panels completes the assembly by acting to provide a watertight seal. There are many other commercial methods of sealing and fastening which also may be used.

The erection and operation of my improved building structure should now be apparent. monocoque panels are simply placed as they will stand in the final structure. Due to their unique configuration and method of forming, they are completely self-supporting. They need only be fastened together from the inside with the fasteners 22 using gasket 23 between panels or by assembling without gaskets. The holes for the fasteners can either be prepunched or drilled at the building site.

Other modifications of the preferred structure will occur to those skilled in the art. For example, in order to produce very wide spans, it may be desirable to manufacture panels in two sections, joining them together along the ridge of the building by a suitable method such as overlapping the half-panels end-to-end and securing them firmly or by riveting or by butting, capping, and bolting.

As shown in FIG. 3, however, it consists of The stressed skin Likewise, the half-panels mentioned above could easily be made wider at the bottom of the building than at the top, still retaining the bi-directional curvature, of course, in order to form an end for the building shown in FIG. 3 or in order to construct a circular enclosure.

FIG. 5 shows a modification or" the joint described in FIG. 4. Instead of allowing the side edges to be directed toward the inside of the enclosure as in FIG. 4, they are formed with a reverse curve as at 26 during stretchforming. This adds to the girder eifect of the panel edges in resisting bending. Since the panel edges are disposed at a greater radius from the center of curvature of the primary arch than portions Z6, they will receive a greater amount of cold working when the panel is stretched and therefore will have greater ultimate strength. It also locates the joining members outside the structure which may be preferable for inside appearance. A compressible gasket 27 similar to that of FIG. 4 may be used, if desired, in order to deaden sound transmission between panels which are fastened together by rivets 28. A U-shaped cap 29 which is preferably of a flexible material such as an extruded vinyl composition may be used to prevent leakage.

It only remains to note that the shape of the panel adapts it to nesting several panels together, whether manufactured as a complete span or in two sections to be joined at the ridge. Also the simplicity of the structure and the need of relatively few parts for erection makes it an ideal structure for summer camps, farm buildings, boat houses, machinery storage, garages, or for temporary use such as emergency disaster area housing, barracks or other shelters.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications which fall within the scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of constructing a self-supporting building structure comprising the steps of: providing a plurality of flat ductile metal sheets each of a length sufiicient for forming both a wall and roof portion of said structure, providing a bi-directionally convex male die defining a gradual major arc with secondary arcs normal thereto, exerting tension at opposite ends of each of said sheets of ductile metal in its longitudinal direction over said die to simultaneously stretch the sheet in a major arc and form the opposite transverse edges of said sheet into substantially parallel flanges, arranging the sheets side-byside with adjacent flange portions extending in the same direction, securing the flange portions of adjacent sheets face-to-face substantially along the entire length thereof, and sealing between the flanges of adjacent sheets to prevent leakage.

2. The method of constructing a self-supporting building structure comprising the steps of: providing a plurality of flat sheets of ductile work-hardenable metal of suflicient length to provide at least part of the sidewall and roof of said structure, providing a bi-directionally convex die, exerting tension on opposite ends of said sheets of metal over said die to are the sheet in its longitudinal direct-ion and to form the transverse edges of the sheet into opposite parallel flanges, providing each of said flanges with longitudinally spaced holes, arranging said sheets side-by-side with adjacent flange portions extending in the same direction, attaching the flanges of the sheets face-to-face with pin fastening means in said holes along substantially the entire flange length, and sealing between said flanges to prevent leakage.

References Cited in the file of this patent UNITED STATES PATENTS 1,903,638 Sykes Apr. 11, 1933 2,006,468 Longren July 2, 1935 2,095,533 Schmidt Oct. 12, 1937 2,215,452 Braglio Sept. 24, 1940 2,279,965 Berliner et al. Apr. 14, 1942 2,318,022 Stolz et a1. May 4, 1943 2,328,197 Cowin Aug. 31, 1943 2,360,831 Drew Oct. 24, 1944 2,378,413 Lermont et a1. June 19, 1945 2,464,169 Bentley Mar. 8, 1949 2,713,376 Bath July 19, 1955 2,850,071 K-raybill Sept. 2, 1958 2,852,109 Pine Sept. 16, 1958 2.871.521 Messmore Feb. 3, 1959 2,933,056 Martin Apr. 19, 1960 OTHER REFERENCES Principles of Stretch-Wrap FormingHutford Machine Works Inc, first edition (1950), pages 58-6 1, 75, 76. 

1. THE METHOD OF CONSTRUCTING A SELF-SUPPORTING BUILDING STRUCTURE COMPRISING THE STEPS OF: PROVIDING A PLURALITY OF FLAT DUCTILE METAL SHEETS EACH OF A LENGTH SUFFICIENT FOR FORMING BOTH A WALL AND ROOF PORTION OF SAID STRUCTURE, PROVIDING A BI-DIRECTIONALLY CONVEX MALE DIE DEFINING A GRADUAL MAJOR ARC WITH SECONDARY ARCS NORMAL THERETO, EXERTING TENSION AT OPPOSITE ENDS OF EACH OF SAID SHEETS OF DUCTILE METAL IN ITS LONGITUDINAL DIRECTION OVER SAID DIE TO SIMULTANEOUSLY STRETCH THE SHEET IN A MAJOR ARC AND FORM THE OPPOSITE TRANSVERSE EDGES OF SAID SHEET INTO SUBSTANTIALLY PARALLEL FLANGES, ARRANGING THE SHEETS SIDE-BYSIDE WITH ADJACENT FLANGE PORTIONS EXTENDING IN THE SAME DIRECTION, SECURING THE FLANGE PORTIONS OF ADJACENT SHEETS FACE-TO-FACE SUBSTANTIALLY ALONG THE ENTIRE LENGTH THEREOF, AND SEALING BETWEEN THE FLANGES OF ADJACENT SHEETS TO PREVENT LEAKAGE. 